Flow cytometry is a well-known technique for counting and/or otherwise examining microscopic particles, such as cells and the like, by passing a stream of fluid in which the particles are suspended through a detection apparatus. The detection apparatus typically relies on detecting the optical response produced as the particles pass through an illuminated region of the device. In prior art microbial flow cytometers, for example, individual particles pass through an illumination zone, typically at a rate on the order of 1,000 cells per second, and detectors, gated electronically, measure the magnitude of a pulse representing the light scattered by the cells. The pulse magnitudes (or other properties) may then be processed to characterize the cells by a particular parameter of interest. For example, the angular dependence of scattered light may provide information on the nature of the scattering particles. More importantly, the fluorescent properties of the particles (which may be caused by appropriate fluorophores being added to the suspension) may provide desired parametric information.
Traditional flow cytometers use a clear sheath fluid to position particles or cells for cytometric measurements. An exemplary flow cytometry system is disclosed, for example, in U.S. Pat. No. 5,760,900, which is hereby incorporated by reference herein in its entirety. A new sheathless flow technology for cytometry systems is disclosed in the inventor's co-pending U.S. patent application Ser. No. 12/027,961 (U.S. Patent Publication No. 2008/0186479), which is hereby incorporated by reference in its entirety.
Flow cytometry has several advantages, including the ability to obtain multi-parametric data and high-speed data acquisition.
The alignment (or tuning) of a flow cytometer typically involves manually aligning the sheath stream (or cuvette) with the optical path of the system and adjusting the position of the light source (e.g., laser) with respect to the measurement or sensing region. The alignment of the flow cytometer can drift due to a number of factors; for example, thermal changes affecting the mechanical components of the system, pointing instability of the laser, and/or external interference, such as mechanical vibrations or the like. After the initial system alignment, the operator is typically tasked with maintaining the alignment, oftentimes making small adjustments to the laser position between each sample. Therefore, the time spent keeping a flow cytometer aligned throughout the day can be significant and the quality of the data between such alignments may be less than optimal.